1. Technical Field
The present invention relates generally to spark ignition systems, and, more particularly, to a drive circuit therefor.
2. Description of the Related Art
Conventional ignition systems for producing a combustion arc across electrodes of a spark plug disposed within a combustion chamber are known, as seen by reference to U.S. Pat. No. 5,692,484 issued to Downey. Downey discloses an inductive ignition system for a multiple cylinder internal combustion engine having an individual ignition coil and spark plug associated with each cylinder, each ignition coil having a primary winding with a first end connected to a power source and a second end, wherein each coil further has a secondary winding connected to a respective spark plug. Downey further discloses a driver device for each coil, particularly an insulated gate bipolar transistor (IGBT) connected between the second end of the primary winding and ground. Thus, Downey discloses an individual driver device for each coil included in the ignition system. An important characteristic of the driver device disclosed in Downey is that each driver device can be independently controlled so as to initiate and discontinue the primary current that flows through the primary winding. Although the drive arrangement disclosed in Downey performs satisfactorily, the driver device, including the associated resistors, capacitors, and voltage clamp devices required for proper implementation results in a relatively costly drive circuit. Moreover, when a well-known darlington is used as the driver device, an additional component, namely a reverse voltage protection component (e.g., an in-line diode disposed in the positive voltage rail supplying the ignition circuit) must further be included, thereby further increasing the cost of the drive circuit.
Less costly current-carrying devices are known, such as silicon-controlled rectifiers (SCR), which are known for use as switches in capacitive (i.e., not inductive) discharge style ignition systems. It is also known to use a bi-directional current carrying device, such as a TRIAC, as seen by reference to U.S. Pat. No. 5,638,799 issued to Kiess et al., also for use in a capacitive (i.e., not inductive) discharge ignition system.
There is therefore a need to provide an improved ignition drive circuit that overcomes one or more of the shortcomings as set forth above.
One object of the present invention is to provide a solution to one or more of the above identified problems. One advantage of the present invention is that it provides a reduced cost ignition system, particularly a reduced cost drive circuit therefor. The invention achieves this by using one main driver for multiple ignition coils rather than multiple drivers. The invention instead uses more cost effective SCRs in each xe2x80x9clegxe2x80x9d(i.e., primary circuit) of the ignition coils as selectors. Another advantage of the present invention is that it reduces or eliminates many of the external components typically required in an ignition drive circuit, such as, for example only, a reverse voltage component, a voltage clamp component, and resistors and capacitors associated with what would otherwise be the added driver devices (but now are not needed). This reduces both component and assembly costs. In yet another embodiment, the main driver is integrated up into a vehicle control module, such as an Engine Control Module (ECM), while the SCRs are integrated in their respective ignition coils. This allows the ECM to provide drive capability and save significant space.
An apparatus according to the invention is provided, suitable for use with an inductive ignition system of a multiple cylinder internal combustion engine having an individual ignition coil and spark plug associated with each cylinder. Each ignition coil has a primary winding with a first end configured for connection to a power source and a second end. Each ignition coil further has a secondary winding configured for connection to a respective spark plug. The apparatus comprises multiple silicon-controlled rectifiers (SCRs), a main driver and a control circuit. An SCR is connected to each ignition coil at the second end of the primary winding, each SCR being controllable into conduction by receipt of a respective gating signal. The other end of each SCR is connected to a common node. The main driver is connected to the SCRs (i.e., at the common node) and is configured to conduct a primary current in response to a drive signal. A control circuit generates the gating signals and the drive signal in timed relationship with each other.
In a preferred embodiment, the main driver is integrated into a vehicle control module, such as an ECM, and the SCRs are integrated with the ignition coils (though this is not necessary). The SCRs are used to select which coil is allowed to carry current when the main driver is turned on. This allows the use of a single main driver, and multiple SCRs as selectors. The SCR also acts as a current block for a reverse battery condition, allowing the use of a darlington transistor component as the main driver without having to add a reverse voltage component, such as diode. As an optional preference, where the main driver may comprise an insulated gate bipolar transistor (IGBT), the use of SCRs allows omitting a voltage clamp (e.g., a zener diode) device on the driver.